The present invention relates to a specific-condition-section detection apparatus and a method of detecting a specific condition section that can be satisfactorily employed when detecting, for example, a black level section in a video signal of broadcast television program.
Due to a significant increase in storage capacity and a reduction in sales price, hard disk devices are not only widely used in personal computers but also in commercial recording and reproducing apparatuses configured to record and reproduce video and audio information of broadcast television programs.
A recording and reproducing apparatus including a hard disk device sometimes also includes a recording and playing drive corresponding to a removable recording medium, such as a digital versatile disk (DVD), so that the recording medium can be handled by the apparatus.
Such a recording and reproducing apparatus may be used in a copy recording process in which a user selects predetermined television programs from the various television programs recorded on a hard disk device of the apparatus and stores the selected television programs on a DVD. The apparatus may also be used in an editing process in which only sections of television programs including predetermined scenes selected by the user are recorded or television programs that are already recorded are re-recorded.
When carrying out such a copy recording process or an editing process on a television program selected by the user, a predetermined television program selected by the user or a predetermined television program that may interest the user is retrieved from the various television programs stored on the hard disk device. However, it is time consuming and inefficient to play the all of the various television programs stored on the hard disk device to retrieve specific sections of the recorded television programs.
To efficiently check the content of recorded video and audio data, the recorded video and audio data can be played in a digest play mode in which the play time is reduced by displaying thumbnails corresponding to predetermined points (i.e., chapter points) of a television program or in a special play mode, such as double-speed play mode, or important sections can be selectively played (i.e., key frames).
To set the above-mentioned predetermined points (i.e., chapter points) of a television program, predetermined characteristic data included the video and audio signals is obtained through a predetermined characteristic extraction process. Then, characteristic points corresponding to important scenes (i.e., key frames) included in the obtained characteristic data are detected. These characteristic points can be set as chapter points.
In the above-mentioned digest playing process, characteristic data is detected in a manner similar to that described above, and then predetermined sections between key frames detected on the basis of the detected characteristic data are played in order, as described in Japanese Unexamined Patent Application Publication No. 2003-219348. In this way, video and audio data can be played in an amount of time shorter than that required for a regular play operation.
Characteristic points included in, for example, a television program and set on the basis of characteristic data detected in a manner described above may be points provided between a main section of the television program and a commercial message (CM) section (i.e., a point provided between the end point of a main section and the start point of a CM section or between the end point of a CM section and the start point of a main section) or points provided between a CM section and another CM section.
For example, Japanese Unexamined Patent Application Publication Nos. 2000-165806 and 2000-165798 disclose techniques for determining CM sections on the basis of CM start points and CM end points determined from silent sections detected in the audio signal and the intervals between the silent sections. Since the lengths of CM sections are integral multiples of about 15 seconds, when the detected silent sections that are specific condition sections appear in intervals of integral multiples of 15 seconds, these silent sections are recognized as CM sections.
Television programs that are played using the recording and reproducing apparatus may include, not only Japanese television programs, but also television programs broadcast in countries other than Japan that also conform to the national television system committee (NTSC) standard, such as the United States.
For example, in case of studying English, although various materials for learning English conversation are commercially available, learners may want to watch US television programs to improve their English listening abilities. In such a case, since US television programs conform to the NTSC standard, learners may record US television programs using a video tape recorder in the United States and play the recorded television program using a Japanese video-playing apparatus.
Since the Internet having a high-speed data transfer rate is now widely used, television programs broadcast in Japan and other countries can be received and recorded via the Internet. Television programs recorded in such a manner may also be played and viewed.
The techniques described in Japanese Unexamined Patent Application Publication Nos. 2003-219348, 2000-165806, and 2000-165798 are related to detection of commercial messages included in television programs broadcast in Japan. The techniques described in these documents cannot be simply employed in a process for detecting commercial messages in television programs broadcast in the United States.
In television programs broadcast in the United States, CM sections cannot be accurately detected by detecting silent sections in the same way as detecting CM sections in television programs broadcast in Japan. To accurately detect CM sections in television programs broadcast in the United States, sections including a plurality of fields having low brightness signal levels and a substantially black level must be detected.
The lengths of CM sections in television programs broadcast in the United States are integral multiple of substantially 15 seconds, which is the same as that in Japan. However, it is known that sections including a plurality of field whose brightness signal levels are the substantially black level (hereinafter referred to as ‘black sections’) are provided at start points and end points of CM sections in US television programs.
Black sections included in CM sections in US television programs and techniques related to CM detection are described in, for example, “Automatic Detection of TV Commercials” (Satterwhite, B.; Marques, O.; Potentials, IEEE, Volume 23, Issue 2, April-May 2004 pp. 9-12). This non-patent document also describes the characteristics of the lengths of the black sections and the CM sections in television programs including commercial messages that have black sections.
As described above, to detect CM sections in television programs broadcast in the United States, black sections must be detected. In general, to detect black sections, sections in which the brightness signal level of the video signal is lower than a reference level that higher than the black level.
Various characteristic points, start points, end points, CM sections, and segments between CM sections, in a video signal were detected by actually viewing television programs broadcast in the United States. As a result, the various characteristic points were detected although noise was present in the signal.
FIG. 40 illustrates the possible waveforms of a brightness signal included in a video signal referred to when detecting a black section corresponding to at least one field. In FIG. 40, the top of the drawing corresponds to the black level, and the bottom the drawing corresponds to the white level. In FIG. 40, Th represents a reference level for comparison. A section in which the signal level exceeds the reference level Th is determined to a black section.
As shown in FIG. 40, a brightness signal 1 has a section in which the signal level is closer to the black level in comparison with the reference level Th for a several fields in a stable manner. A black section can be stably detected in such a brightness signal. In the case of the waveform 1 in FIG. 40, the section from field number f1 to field number f2 is detected as a black section.
In contrast, as shown in FIG. 40, although a brightness signal 2 includes a black section, in some field segments included in the brightness signal, the signal level is closer to the white level compared to the reference level Th due to an influence of noise. In other words, the brightness signal has a fluctuating waveform. In the case of the brightness signal 2 in FIG. 40, although the actual black section is the section from field number f3 to field number f4, the black section cannot be detected accurately.
As shown in FIG. 40, a brightness signal 3 includes a short black section. The length of the black section in which the signal level is closer to the black level compared to the reference level Th is, for example, one field. The black section is the section from field number f5 to field number f6.
As shown in FIG. 40, a brightness signal 4 having a signal level that is only slightly closer to the black level compared to the reference level Th. In this case, the section from field number f7 to field number f8 can be detected as a black section.
As shown in FIG. 40, a brightness signal 5 having a step-like waveform. In this case, if the black section is detected on the basis of whether or not the signal level is closer to the black level compared to the reference level Th, the section from field number f9 to field number f11 will be detected as a black section. However, it is more desirable to employ a detection method that is able to detect the section from field number f9 to field number f10 that is closer to the black level than the section from field number f10 to field number f11 as a black section.
As the brightness signals 1 to 5 shown in FIG. 40, a black section may not be accurately detected in a video signal of a television program when detection is carried out by simply comparing the brightness level and a reference level Th.
The waveforms of the signals 1 to 5 shown in FIG. 40 are not limited to the waveforms of brightness signals of a television program used to detect black sections but are also waveforms observed in any type of data signals used for detecting specific condition sections in which the signal level is closer to a predetermined signal level compared with a reference level.